The present invention relates to techniques for scanning and reproducing images and, more particularly, to techniques for processing scanned image data to generate a digital image for display or reproduction.
Creation of positive images from photographic negatives can be a difficult and imprecise process. The fundamental problem is that the consumer wants to receive images that are consistently the correct color balance and brightness despite variables in the photographic imaging process. Sources of variation in the photographic imaging process include: (a) variations in spectrophotometric and sensitometric characteristics from film type to film type, (b) emulsion to emulsion variation within a film type, due to film manufacturing variability, film shelf aging before exposure, latent image fading after exposure, dark fading after processing, and chemistry variations in the film processing step, (c) illumination variation at the time of photography, which can cause both color balance variation in the image and exposure level variation, and (d) other variations, such as those arising from camera lens color differences. The challenge in photographic color correction is compensating for each of the above variables, while at the same time preserving color deviations from neutral in the image that are caused by the subject matter that was photographed.
The present invention is directed to a system and method for correction and reconstruction of color images generated by a scanner. The system and method make use of one or more of a set of algorithms for color calibration and correction, and reconstruction of scanned images. The images can be scanned, for example, from reflective or transmissive film or paper. In particular, the images can be scanned from processed negative or positive photographic film. Other examples include photothermographic or thermographic film, electrographically printed paper, inkjet printed paper, and the like. For ease of illustration, all of the above media will be referred to herein as xe2x80x9cfilm.xe2x80x9d
In a photographic film application, for example, a color calibration and correction algorithm enables correction of the image for variations in hue from film type to film type, over-exposure or under-exposure, exposure-induced hue shifts, hue shifts caused by lighting effects, processing related hue shifts, and other variables in film processing, while preserving overall hue of the subject matter in the originally photographed image. An image reconstruction algorithm allows creation of look-up tables (LUTs) that create a visually pleasing version of the image when applied to the original data. If desired, the system and method also may use an algorithm for optimized bit depth reduction that more effectively matches the response curve of the scanner to that of the film, thereby improving signal-to-noise ratio and decreasing artifacts such as pixelization, which can result from sampling the tone curve too coarsely.
In one embodiment, the present invention provides a method for correcting a digital color image scanned from film, the method comprising producing average color value data for the scanned color image, performing exposure correction of the image using the average color value data and exposure calibration data, performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction, generating image correction data representative of the exposure correction and the chromatic correction, and applying the image correction data to the image to produce a corrected color image.
In another embodiment, the present invention provides a system for correcting a digital color image scanned from film, the system comprising means for producing average color value data for the scanned color image, means for performing exposure correction of the image using the average color value data and exposure calibration data, means for performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction, means for generating image correction data representative of the exposure correction and the chromatic correction, and means for applying the image correction data to the image to produce a corrected color image.
In a further embodiment, the present invention provides a method for reconstructing a digital color image scanned from film, the method comprising producing average RGB color value data for the scanned color image, performing exposure correction of the image using the average color value data and exposure calibration data, performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction, generating image correction data representative of the exposure correction and the chromatic correction, generating reconstruction lookup tables (LUTs) based on the color correction data and the average color value data, each of the reconstruction LUTs representing a curve for reconstruction of one of the RGB color channels for the image, and applying each of the reconstruction LUTs independently for the respective RGB color channels to produce a reconstructed color image.
In an added embodiment, the present invention provides a system for reconstructing a digital color image scanned from film, the system comprising means for producing average RGB color value data for the scanned color image, means for performing exposure correction of the image using the average color value data and exposure calibration data, means for performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction, means for generating image correction data representative of the exposure correction and the chromatic correction, means for generating reconstruction lookup tables (LUTs) based on the color correction data and the average color value data, each of the reconstruction lookup tables representing a curve for reconstruction of one of the RGB color channels for the image, and means for applying each of the reconstruction LUTs independently for the respective RGB color channels to produce a reconstructed color image.
In another embodiment, the present invention provides a method for correcting a digital color image scanned from film, the method comprising producing average color value data for the scanned color image, performing exposure correction of the image using the average color value data and exposure calibration data, performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction, generating image correction data representative of the exposure correction and the chromatic correction, and applying the image correction data to the image to produce a corrected color image.
In a further embodiment, the present invention provides a system for correcting a digital color image scanned from film, the system comprising means for producing average color value data for the scanned color image, means for performing exposure correction of the image using the average color value data and exposure calibration data, means for performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction, means for generating image correction data representative of the exposure correction and the chromatic correction, and means for applying the image correction data to the image to produce a corrected color image.
Other advantages, features, and embodiments of the present invention will become apparent from the following detailed description and claims.